A variety of non-linear structures exhibit negative mechanical stiffness, such as snap-through beams and buckling beams. Negative stiffness may also be exhibited by various combinations and arrangements of springs and/or beams with pinned or clamped boundaries. For instance, negative stiffness may be exhibited due to over-rotation of one of the components, or rolling or sliding contact between components. Negative stiffness mechanisms are useful in a variety of applications, including vibration isolation, shock mitigation, and signal processing.
However, many related art negative stiffness mechanisms do not incorporate a variable negative stiffness spring. For instance, related art negative stiffness mechanisms may incorporate an external cam to change the effective length of a lever attached to a variable stiffness spring or a variable pivot point for a leveraged spring. Other related art negative stiffness mechanisms include a variable stiffness spring having a lever supported by antogonistic non-linear springs (e.g., rubber cones). However, each of these related art negative stiffness mechanisms are incapable of supporting a significant load when the mechanism is soft, which make them of limited use as an isolator.
Additionally, other related art negative stiffness mechanisms may incorporate pneumatic, hydraulic, hydropneumatic, voice coil, and/or piezoelectric components. However, related art negative stiffness mechanisms that incorporate pneumatic components may require large volume air springs and high-friction seals, which prevent isolation of low amplitude vibrations. Additionally, related art negative stiffness mechanisms that incorporate voice coil or piezoelectric components may not be capable of isolating larger amplitude vibrations.